1. Field of the Invention
This invention relates to a conducting roller for an electroplating apparatus, more particularly to a two-input type conducting roller which has two ends that accept simultaneously electric current so as to form a uniform-diameter metal coating on a circuit board.
2. Description of the Related Art
Referring to FIG. 1, a conventional electroplating apparatus is shown to include pairs of conducting rollers 7 disposed at upstream and downstream sides of an electroplating bath 9, which contains an electrolyte. A plurality of spray tubes 91, 92 and roller units 93 are provided inside the electroplating bath 9. The spray tubes 91, 92 not only function as anodes as they are connected electrically to a power source, but also spray an electrolyte onto a horizontal circuit board 8. Each of the roller units 93 includes a plurality of upper rollers 931 and a lower roller 932 to advance the board 8 through the electroplating bath 9. The upper rollers 932 are arranged such that they will move downward by gravity to place the lowermost upper roller 931 in contact with the corresponding lower roller 932 as soon as the board 8 moves past the inlet 94 and outlet 94 of the electroplating bath 9, thereby sealing the inlet 94 and the outlet 94 and preventing the electrolyte from leaking and from staining the conducting rollers 7 provided outwardly of the electroplating bath 9.
FIG. 2 shows one conducting roller 7, which includes a rotatable conductive roller body 71 that presses against a side surface of the board 8 (see FIG. 1), and a stationary conducting rod 72 that is inserted into a chamber 711 in a left end portion of the roller body 71. The chamber 711 has two ends 712, 713, which are provided with a pair of bearing members 714, on which the conducting rod 72 is journalled. The roller body 71 is rotated by means of a gear unit 715. An annular seal 73 is sleeved on the conducting rod 72 so as to seal the chamber 711. A conductive liquid 74 is filled in the chamber 711 between the roller body 71 and the conducting rod 72. As such, electric current can be transmitted from the conducting rod 72 to the roller body 71 via the conductive liquid 74. The disadvantages of the conducting roller 7 are as follows:
(1) A resistance loss is incurred on the roller body 71, and increases gradually from the left end to the right end in view of the condition that only a single cathode current input is provided to the left end of the roller body 71, thereby resulting in an uneven thickness of metal coating on the board 8.
(2) The conductive liquid 74 is normally made of mercury, which is highly poisonous, thereby resulting in serious environmental protection problems caused during filling and throwing-away thereof. Thus, it is desirable to reduce the amount of the conductive liquid 74 used in the roller body 71. However, because the conducting rod 72 is relatively long, a substantial amount of the conductive liquid 74 needed to fill in the chamber 711.
An object of this invention is to provide a two-input type conducting roller for an electroplating apparatus, which has a constant voltage value at all of the axial positions thereof so as to maintain an even distribution of cathode current to an electrolyte, thereby forming effectively a uniform-diameter metal coating on a circuit board.
Another object of this invention is to provide a two-input type conducting roller for an electroplating apparatus, which needs only a small amount of conductive liquid to be used therein.
According to this invention, a conducting roller is used in an electroplating apparatus, and includes a conductive roller body, which has two diameter-reduced end portions that are journalled within two stationary conductive sleeve units. A conductive liquid is filled within two sealed gaps between the end portions of the roller body and the sleeve units, thereby transmitting cathode current from the conducting sleeve units to the end portions of the roller body.
Because cathode current is input simultaneously to the end portions of the roller body, the voltage value of the roller body is constant at all of the axial positions thereof such that a uniform-diameter of metal coating can be formed on a circuit board.
Furthermore, the sealed gaps are relatively small such that the amount of the conductive liquid required to be used in the conducting roller can be reduced.